create simple collimated beam

[Jaap1957]

Hi,
This must be a very simple question for this forum.
up to now i used a pencil beam source,
particles come from 1 point at z = +1 meter and move down the z axis.

:start source:
name = pencil_beam
library = egs_parallel_beam
charge = -1 ## for electron
direction = 0 0 -1 ## -z direction
:start spectrum:
type = monoenergetic
energy = 0.3 # in MeV
:stop spectrum:
:start shape:
type = point
position = 0 0 100 # in cm : z=+1m
:stop shape:
:stop source:

Now i want to step up to a rectangular plane source.
Particles move parallel, same z starting plane, same direction, only from a rectangle of 2x2 cm
I tried:

:start source:
name = a_parallel_beam
library = egs_parallel_beam
:start shape:
library = egs_rectangle
rectangle = -1 -1 1 1
position = 0 0 100
:stop shape:
:start spectrum:
type = monoenergetic
energy = 0.3
:stop spectrum:
direction = 0 0 -1
charge = -1
:stop source:

This does not work since the egs_rectangle only knows about x and y and not about position in z direction.

How do I get EGS to start particles from a rectangle -1 -1 1 1 at z = +100 ?

[Jaap1957]

https://www.reddit.com/r/EGSnrc/comments/n38tvs/collimated_source_collapses_near_origin/
tells me to add a transformation, thanks again mr Townson !

This works, to get a rectangle at z = +10 cm of 2x2 cm sending electrons down the z axis .

:start source definition:
:start source:
       library = egs_parallel_beam
       name = a_parallel_beam
       :start shape:
            library = egs_rectangle
            rectangle = 1 1 -1 -1
            # rectangles are always at z=0 ... 
            :start transformation:
                translation = 0 0 +10    
            :stop transformation:
       :stop shape:
       :start spectrum:
         type = monoenergetic
         energy = 0.3
       :stop spectrum:
       direction = 0 0 -1
       charge = -1
   :stop source:
    simulation source = a_parallel_beam
:stop source definition: